The limits are reasonable to prevent exposure to fraud losses. Also, there are varying money laundering laws that look a lot like those limits.

They are still quite liquid in BTC deposits at least: if you look at this address that had 470k BTC at one point, you see that the coins are still there, just moved to a bunch of 50k accounts. They probably have dollar deposits within an order of magnitude of that.

They have a solid business moving currencies back and forth between accounts in their system with ~0.5% fees each time. You move 100BTC to dollars and back 69 times, now they have 50BTC and you have 50BTC. As long as traders leave BTC and dollars in mtgox and trade amongst themselves, the amount of those funds that now belong to mtgox from fees just keeps increasing...

Also, there are varying money laundering laws that look a lot like those limits.

such as??

for instance, the in the United States, only CASH deposits (or withdrawals) of the arbitrary amount of $10,001 or greater are subject to any "limit". Cash meaning printed federal reserve notes. Not anything electronic, or check, or anything.

And this limit means simply filling out a federal form stating that this transaction happened. (Currency Transaction Report, CTR)

there is no limit or prohibition to those large amounts. but it is a crime to not have the CTR done or to try and avoid it via structuring.

Mt Gox is in japan right? I dont think japan has more restrictive cash controls than america, if any

there could be some regulatory issue - such as the OP mentioned - liquidity, fractional reserve